18.3 The Krebs Cycle

Question 1

Outline the processes occuring in the Krebs cycle:

Answer 1

1. Acetyl coenzyme A delivers acetyl group to Krebs Cycle
   
   1. Acetyl group (2 carbon) + Oxaloacetate (4 carbon) ⟶ Citrate (6 carbon)
2. Citrate undergoes decarboxylation & dehydrogenation ⟶ 5 carbon compound + CO2 + Reduced NAD
3. 5 carbon compound undergoes further decarboxylation & dehydrogenation ⟶ regenerate oxaloacetate
   
   1. Phosphorylates ADP, releases CO2 + reduced NAD

Cycle continues

Question 2

How many of each product is produced per cycle of the Krebs cycle?

Answer 2

• 3 Reduced NAD (NADH)
• 1 Reduced FAD (FADH₂)
• 1 ATP (from substrate-level phosphorylation)

Question 3

What is a coenzyme?

Answer 3

molecule which transfers atom(s)

from 1 reaction to another

in a multi-step pathway

Question 4

What are the coenzymes involved in the Krebs cycle?

Answer 4

NAD + FAD + Coenzyme A

Question 5

What are the differences between NAD & FAD?

Answer 5

• NAD involved in all stages of cellular respiration, but FAD only involved in Krebs cycle
• NAD accepts 1 hydrogen atom, but FAD accepts 2 to become reduced FAD
• Reduced NAD oxidised at beginning of electron transport chain, reduced FAD is oxidised further along
• Reduced NAD synthesises 3 ATP molecules, Reduced FAD synthesises only 2 ATP molecules

Question 6

Where are coenzymes derived from?

Answer 6

vitamins

Question 7

How many carbon atoms does oxaloacetate contain?

Answer 7

4

Question 8

How many carbon atoms does an acetyl group contain?

Answer 8

2